A technique that combines laser light with ultrasound can provide high-resolution images of anatomic structures and chemical activities, such as oxygen metabolism, deep in tissue.

Engineers from Washington University in St. Louis have developed an imaging technology called photoacoustic tomography that allows scientists to produce high-resolution images of anatomic structures and chemical activities concealed under centimeters of flesh (Science 2012;335:1458–62).

One goal for the technology is “to detect very-early-stage cancer, such as during colonoscopy or skin or breast cancer screens,” says principal investigator and bioengineer Lihong Wang, PhD. “By combining anatomic structure with functional and metabolic information, we hope to make a much more accurate diagnosis.”

A technique that combines laser light with ultrasound can provide high-resolution images of anatomic structures and chemical activities, such as oxygen metabolism, deep in tissue. Here, photoacoustic tomography reveals a renal tumor xenograft at a depth of 2 mm (red) in a mouse ear (yellow). [Photo courtesy of Song Hu, Jeff Arbeit, and Lihong Wang]
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A technique that combines laser light with ultrasound can provide high-resolution images of anatomic structures and chemical activities, such as oxygen metabolism, deep in tissue. Here, photoacoustic tomography reveals a renal tumor xenograft at a depth of 2 mm (red) in a mouse ear (yellow). [Photo courtesy of Song Hu, Jeff Arbeit, and Lihong Wang]

A technique that combines laser light with ultrasound can provide high-resolution images of anatomic structures and chemical activities, such as oxygen metabolism, deep in tissue. Here, photoacoustic tomography reveals a renal tumor xenograft at a depth of 2 mm (red) in a mouse ear (yellow). [Photo courtesy of Song Hu, Jeff Arbeit, and Lihong Wang]
View largeDownload slide

A technique that combines laser light with ultrasound can provide high-resolution images of anatomic structures and chemical activities, such as oxygen metabolism, deep in tissue. Here, photoacoustic tomography reveals a renal tumor xenograft at a depth of 2 mm (red) in a mouse ear (yellow). [Photo courtesy of Song Hu, Jeff Arbeit, and Lihong Wang]

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Designed to detect and image different molecules, such as hemoglobin in red blood cells or melanin in skin, photoacoustic tomography blends light with ultrasound. First, researchers shine a pulse of laser light tuned to a given wavelength into the tissue. Molecules that absorb light of that color create a thermally induced pressure jump that creates a sound wave, which is captured using ultrasound detectors. To see another type of molecule, the investigators tune the laser to a different color.

Taken together, the data paint exquisite high-contrast images that clearly reveal and differentiate arteries, veins, and—with the help of injected dyes—tumor and other tissues. The data also reveal biochemical activities. For instance, because oxygenated and deoxygenated hemoglobin produce different colors, snapshots taken with 2 different laser colors can be compared and used to calculate the metabolic rate of oxygen for a given region of the body.

In previous work, Wang and colleagues used this technique to detect a doubling of oxygen metabolism just 1 week after implanting tumors in animal models.

Currently, the technology penetrates up to 7 cm through tissue. Because it operates well within accepted safety limits for laser and ultrasound devices, Wang sees the potential for the technology to reach deeper. Clinical trials are under way in collaboration with radiologists at Washington University School of Medicine to evaluate the use of photoacoustic tomography to gauge the efficacy of chemotherapy for breast cancer. Standard procedures monitor tumor structure, which changes slowly. By also monitoring functional and metabolic activity, it may be possible to predict efficacy in a span of weeks rather than months.

In addition, trials are planned to noninvasively assess the depth and volume of melanoma tumors and to reveal blood vessel density, oxygen saturation, and metabolic rates.

For more news on cancer research, visit Cancer Discovery online at http://CDnews.aacrjournals.org.

©2012 American Association for Cancer Research.
2012